1. Field of the Invention
This invention relates to a vibration wave driving apparatus applied to a so-called vibration wave motor which generates vibration on an elastic member by an electromechanical energy converting element for converting an electrical amount (voltage) into a mechanical amount (vibration), and moves a contact member contacting with the elastic member.
2. Related Background Art
There has heretofore been a vibration wave motor for driving a moving element by vibration generated by a vibration element. The vibration wave motor produces a force continuously driving the moving element, by the use of mechanical vibration generated by the vibration element. Therefore, a contact member disposed between the vibration element and the moving element repeats contact with and separation from the vibration element while being deformed following the vibration of the vibration element, thereby producing a driving force. A vibration wave motor of this kind is shown in FIG. 14 of the accompanying drawings.
FIG. 14 is a cross-sectional view showing the construction of a vibration wave motor according to Japanese Patent Application Laid-open No. 2001-145376.
In FIG. 14, the vibration wave motor is a known bar-shaped vibration wave motor of a construction in which a moving member 105 is brought into pressure contact with a vibration element. The vibration element has a construction in which a shaft 104 is inserted into the inner diameter portions of a piezoelectric element 103 and metal members 101, 102, and the piezoelectric element 103 is sandwiched between the metal members 101 and 102 and is bolt-fastened by the shaft 104. A plurality of contact portions 105a having such predetermined spring rigidity that some area thereof contacts relative to the vibration of the vibration element are fixed to the moving member 105. The reference characters 101d and 101e designate the inner side portion and outer side portion, respectively, of the metal member 101, the reference character 101a denotes a connecting portion between the inner side portion and the outer side portion, the reference character 101f designates an aperture portion for a wiring substrate, the reference character 101b denotes a contact surface, the reference numeral 111 designates a wiring substrate, and the reference numeral 119 denotes a hoop for fixing the contact portions.
Each contact portion 105a is of a shape extending inwardly obliquely from the base of the cylindrically shaped moving member 105, and the extending portions can be independently deformed without contacting with one another. When surface pressure applied to the frictionally sliding portion of each contact portion with the metal member 101 becomes high, abrasion is aggravated. If the frictionally sliding portion is simply widened to mitigate this, portions which do not coincide with vibration displacement increase therein, thus resulting in the cause of abrasion, squeak or the like. In the prior art, each contact portion 105a is independently displaced and therefore, it becomes possible to make each contact portion 105a coincident with vibration displacement, and it is possible to easily construct a vibration wave motor of great torque. The displacement direction of the contact portions 105a is indicated by arrow in FIG. 14.
FIG. 16A of the accompanying drawings shows a case where the vibration displacement of the vibration member of the vibration wave motor has a smooth distribution in the circumferential direction thereof, and FIG. 16B of the accompanying drawings shows a case where the vibration displacement of the vibration member of the vibration wave motor is forced displacement concentrating in a portion.
In FIGS. 16A and 16B, in the contact portion of the vibration wave motor, there is obtained a contact reaction force (pressure reaction force) substantially proportional to vibration displacement in a case where as shown in FIG. 16A, the vibration displacement of the vibration member has a smooth distribution in the circumferential direction thereof. However, in a case where as shown in FIG. 16B, the vibration displacement of the vibration member is forced displacement concentrating in a portion, the surroundings of the forced displacement portion are also deformed because the contact portion is a circumferentially continuous beam. As the result, a reaction force corresponding to the area of which the deformation has been caused works, and the contact reaction force (pressure reaction force) due to the forced displacement increases. The concentration of such a contact reaction force may become the cause of the localized abrasion or abnormal vibration of a material producing friction in the vibration member and the contact portion, and may spoil the performance of the vibration wave motor.
FIGS. 15A and 15B of the accompanying drawings show the contact portion of a vibration wave motor according to another example of the prior art.
FIG. 15A shows the contact portion of a vibration wave motor according to Japanese Patent Application Laid-open No. 2002-315364. FIG. 15B is an enlarged view of a portion of the contact portion 205 of FIG. 15A.
In FIGS. 15A and 15B, the distal end portion of the contact portion 205 is divided into a plurality of slits. By dividing the distal end portion into a plurality of slits, it becomes possible to suppress the deformation in the contact area of the contact portion 205 with a vibration element from reaching other regions, and reduce an increase in the abrasion due to the above-mentioned concentration of the contact reaction force or the distortion of a frictional surface.
However, the contact portion of the vibration wave motor according to an example of the prior art shown in FIG. 14 is constituted by a plurality of contact portions 105a, but the cross section of each contact portion 105a is a cantilever cross section having a predetermined contact width. Each contact portion 105a contacts with the vibration element, as shown in FIG. 17 of the accompanying drawings.
The angle formed by and between the contact surface of the vibration element and the contact portion 105a when the contact portion is displaced becomes greater as the displacement becomes greater, and only the edge portions of the contact portions 105a come into contact with the vibration element with strong pressure. Therefore, it becomes necessary to reduce the pressure force of the whole against the vibration element so that stable abrasion may also occur in the edge portions of the contact portions 105a contacting with the vibration element with strong pressure. Output torque may be considered to be substantially proportional to the pressure force and thus, the output torque of the vibration wave motor is limited.
On the other hand, the contact portion 205 of the vibration wave motor according to another example of the prior art shown in FIGS. 15A and 15B can reduce the concentration of a reaction force by being divided into a plurality of slits. However, this vibration wave motor is similar to the vibration wave motor according to an example of the prior art shown in FIG. 14 in that the contact portion 205 is of cantilever structure, and there is the undesirable possibility that localized abrasion may be caused by such a contact state between the vibration element and the contact portion as shown in FIG. 17 to thereby deteriorate the performance of the vibration wave motor.
Further, in the contact portion, it is necessary to follow up to a sufficiently high frequency relative to the driving frequency of the vibration element to thereby keep stable contact, but when the contact portion is divided as shown in FIGS. 15A and 15B, the rigidity of each contact portion is reduced and the follow-up property becomes bad. Therefore, to keep the follow-up properties of the contact portions equal to each other, it becomes necessary to make the contact portions into a more minute shape, but this requires much time and labor for manufacture, and results in a higher cost.
As described above, in the construction of the conventional vibration wave motor, there is the problem that durability is reduced by the localized abrasion between the vibration element and the contact portion. Consequently, it is considered that room for improvements is left about reducing the localized abrasion of the contact member to thereby reduce the deterioration of performance due to long-term driving.